Novel phosphorus-containing monomers and flame retardant high impact monovinylidene aromatic polymer compositions derived therefrom

ABSTRACT

Disclosed are cyclic phosphate esters of fumarate—or maleic acids suitable for use as a comonomer, capable of being copolymerized with a monovinylidene aromatic compounds to impart flame resistant properties to the resultant copolymers.

CROSS REFERENCE STATEMENT

[0001] This application is a Divisional of U.S. application Ser.No.09/912,083, filed Jul. 24, 2001, which claims the benefit of U.S.Provisional Application No. 60/220927, filed Jul. 27, 2000, nowabandoned.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to a number of novelphosphorus-containing monomers capable of imparting flame resistantproperties to certain high impact polymer compositions synthesized usingsuch monomers.

[0003] Polymers derived from a monovinylidene aromatic compound, such asstyrene, have successfully been used commercially in numerous end-useapplications for a number of years. Such polymers include the highimpact modifications thereof in which the impact strength is improved byincorporating a minor amount of a toughening agent, such as a suitablerubber, during the polymerization. One major disadvantage of suchpolymers is their inherent high flammability. A well-known approach todeal with the flammability has been to incorporate various flameretardant additives to the polymers. A well-known group of suchadditives are certain halogenated flame retardant organic compounds suchas decabromodiphenyloxide.

[0004] When such halogenated organic compounds are blended with polymersderived from a monovinylidene aromatic compound, the flammability of theresultant polymer compositions is significantly diminished. However,such halogenated compounds also present potential problems associatedwith toxicity and environmental impact. To overcome such problems,certain phosphorus-containing compounds such as triphenylphosphate havebeen used in lieu of halogenated compounds. Despite their proven utilityas flame retardant additives for polymers of a monovinylidene aromaticcompound, such phosphorus-containing compounds have several knowndisadvantages. More particularly, such compounds have a tendency to bevolatilized and thereby lose their overall effectiveness as flameretardant additives, when polymers blended therewith are beingfabricated into useful articles. Such compounds also tend to migrate tothe surface of fabricated articles and plate out on the surface ofpolymer processing equipment in a phenomenon known in the trade as“juicing.” Further, any extra amounts of such compounds used in polymerblends to compensate for the loss of their effectiveness because of theknown volatility often tend to plasticize polymer blends therebyadversely impacting certain physical properties thereof such as heatresistance.

[0005] Therefore, it remains highly desirable to obtain a monovinylidenearomatic polymer composition having effective flame resistance withoutdisadvantages of previous attempts therefor and related flame retardantadditives known in the prior art.

SUMMARY OF THE INVENTION

[0006] One aspect of the present invention is a phosphorus-containingcompound suitable for use as a comonomer, capable of being copolymerizedwith monovinylidene aromatic compounds to impart flame resistantproperties to the resultant copolymers thereof, comprising compounds ofa generic formula:

[0007] wherein:

[0008] R₁ is hydrogen or an alkyl;

[0009] R₂ is carboalkoxy;

[0010] X is oxygen, sulfur or alkylamine;

[0011] P is trivalent phosphorus ; and

[0012] n is 2 or 3.

[0013] Another aspect of the present invention is thephosphorus-containing compound of the generic formula above wherein R2is a radical having a generic formula:

[0014] wherein:

[0015] R₁ is hydrogen or an alkyl;

[0016] X is oxygen, sulfur or alkylamine;

[0017] P is trivalent phosphorus ; and

[0018] n is 2 or 3.

[0019] Yet another aspect of the present invention is aphosphorus-containing compound suitable for use as a comonomer, capableof being copolymerized with a monovinylidene aromatic compounds toimpart flame resistant properties to the resultant copolymers thereof,comprising compounds of a generic formula:

[0020] wherein:

[0021] R₁ is hydrogen or an alkyl;

[0022] R₂ is carboalkoxy;

[0023] X is oxygen, sulfur or alkylamine;

[0024] Y is oxygen or sulfur;

[0025] P is pentavalent phosphorus ; and

[0026] n is 2or3.

[0027] Another aspect of the present invention is thephosphorus-containing compound of the generic formula above wherein R2is a radical having a generic formula:

[0028] wherein:

[0029] R₁ is hydrogen or an alkyl;

[0030] X is oxygen, sulfur or alkylamine;

[0031] Y is oxygen or sulfur;

[0032] P is pentavalent phosphorus ; and

[0033] n is 2 or 3.

[0034] Another aspect of the present invention is a flame retardant (co)polymer composition of a monovinylidene aromatic compound aphosphorus-containing compound of the generic formula, which may betoughened or modified with rubber or other elastomers.

DETAILED DESCRIPTION OF INVENTION

[0035] Phosphorus-containing monomers of the present invention cangenerally be categorized as cyclic phosphonite or phosphonate containingesters of fumaric and maleic acid. Synthesis of relevant monomers orcompounds of the present invention are well within the capabilities ofthose skilled in the art.

[0036] Examples of useful compounds of the present invention, asidentified in accordance with the nomenclature system of ChemicalAbstracts, include, without limitation: 2-Butenedioic acid (2E)-, bis[(5,5-dimethyl-1,3,2-dioxaphosphorinan-2-yl)methyl] ester; 2-Butenedioicacid: 2-methyl-, 4-[(5,5-dimethyl-1,3,2-dioxaphosphorinan-2-yl)methyl]1-methyl ester, (2E)-; 2-Propenoic acid,(5,5-dimethyl-2-oxido-1,3,2-dioxaphosphorinan-2-yl)methyl ester;2-Propenoic acid, 2-methyl-,(4,4,5,5-tetramethyl-1,3,2-dioxaphospholan-2-yl)methyl ester;2-Propenoic acid,1-(5,5-dimethyl-2-sulfido-1,3,2-dioxaphosphorinan-2-yl)ethyl ester; and2-Propenoic acid,(tetrahydro-1,3,5,5-tetramethyl-2-oxido-1,3,2-diazaphosphorin-2(1H)-yl)methyl ester.

[0037] Monovinylidene aromatic polymers suitable for use as a matrix inthe preparation of the rubber modified monovinylidene aromatic polymerare those produced by polymerizing a vinyl aromatic monomer. Vinylaromatic monomers include, but are not limited to those described inU.S. Pat. No. 4,666,987, U.S. Pat. No. 4,572,819 and U.S. Pat. No.4,585,825, which are herein incorporated by reference. Preferably, themonomer is of the formula:

[0038] wherein R is hydrogen or methyl, Ar is an aromatic ring structurehaving from 1 to 3 aromatic rings with or without alkyl, halo, orhaloalkyl substitution, wherein any alkyl group contains 1 to 6 carbonatoms and haloalkyl refers to a halo substituted alkyl group.Preferably, Ar is phenyl or alkylphenyl, wherein alkylphenyl refers toan alkyl substituted phenyl group, with phenyl being most preferred.Typical vinyl aromatic monomers which can be used include: styrene,alpha-methylstyrene, all isomers of vinyl toluene, especiallyparavinyltoluene, all isomers of ethylstyrene, propylstyrene, vinylbiphenyl, vinyl naphthalene, vinyl anthracene and the like, and mixturesthereof. The vinyl aromatic monomers may also be combined with othercopolymerizable monomers. Examples of such monomers include, but are notlimited to acrylic monomers such as acrylonitrile, methacrylonitrile,methacrylic acid, methyl methacrylate, acrylic acid, and methylacrylate; maleimide, n-phenylmaleimide, and maleic anhydride. Thesecopolymerizable monomers can be used alone or in combination. Forexample, a phosphorus-containing compound of the present invention canbe copolymerized with a monovinylidene aromatic compound in combinationwith at least one copolymerizable monomer(s) to produce copolymers ofthe present invention. A preferred copolymerizable monomer isacrylonitrile. A preferred combination of copolymerizable monomerscomprise acrylonitrile and n-phenylmaleimide.

[0039] The polymerization of the vinyl aromatic monomer is conducted inthe presence of predissolved elastomer to prepare impact modified, orgrafted rubber containing products. Rubber modified vinyl aromaticpolymers can be prepared by polymerizing the vinyl aromatic monomer inthe presence of a predissolved rubber to prepare impact modified, orgrafted rubber containing products, examples of which are described inU.S. Pat. No. 3,123,655, U.S. Pat. No. 3,346,520, U.S. Pat. No.3,639,522, and U.S. Pat. No. 4,409,369 which are herein incorporated byreference. The rubber is typically a butadiene or isoprene rubber,preferably polybutadiene. Preferably, the rubber modified vinyl aromaticpolymer is high impact polystyrene (HIPS) oracrylonitrile-butadiene-styrene (ABS), with HIPS being most preferred.

[0040] The rubber particles typically have a volume average particlesize of from 0.2 to 3.0 microns. If a bimodal particle size is produced,the rubber typically comprises from approximately 80 to 85 weightpercent of the aforementioned particles and from about 5 to 20 weightpercent of particles having a volume average particle size of from 2 to6 microns.

[0041] The polymerization is preferably conducted in the presence of aninitiator. Suitable initiators include any initiator capable ofimparting the desired grafting of polymer to the rubber particle underthe conditions of polymerization and accelerating the polymerization ofthe vinyl aromatic monomer. Representative initiators include peroxideinitiators such as peresters, e.g. tertiary butyl peroxybenzoate andtertiary butyl peroxyacetate, tertiary butyl peroxyoctoate, dibenzoylperoxide, dilauroyl peroxide, 1.1-bis tertiarybutyl peroxycyclohexane,1-3-bis tertiarybutylperoxy-3,3,5-trimethyl cyclohexane, di-cumylperoxide, and the like. Photochemical initiation techniques can beemployed if desired. Preferred initiators include tertiary butylperoctoate, tertiary butyl isopropyl percarbonate, dibenzoyl peroxide,tertiary butyl peroxy benzoate, 1,1-bistertiarybutylperoxy cyclohexaneand tertiarybutylperoxy acetate.

[0042] Initiators may be employed in a range of concentrations dependenton a variety of factors including the specific initiators employed, thedesired levels of polymer grafting and the conditions at which the masspolymerization is conducted. Typically, initiators may be employed inamounts from 0 to 2000, preferably from 100 to 1500, parts by weight permillion parts by weight of vinyl aromatic monomer.

[0043] Additionally, a solvent may be used in the polymerization.Acceptable solvents include normally liquid organic materials which forma solution with the rubber, vinyl aromatic monomer and the polymerprepared therefrom. Representative solvents include substituted aromatichydrocarbons such as ethylbenzene, toluene, xylene or the like;substituted or unsubstituted, straight or branched chain saturatedaliphatics of 5 or more carbon atoms, such as heptane, hexane, octane orthe like; alicyclic or substituted alicyclic hydrocarbons having 5 or 6carbon atoms, such as cyclohexane; and the like. Preferred solventsinclude substituted aromatics, with ethylbenzene and xylene being mostpreferred. In general, the solvent is employed in amounts sufficient toimprove the processability and heat transfer during polymerization. Suchamounts will vary depending on the rubber, monomer and solvent employed,the process equipment and the desired degree of polymerization. Ifemployed, the solvent is generally employed in an amount of up to about35 weight percent, preferably from about 2 to about 25 weight percent,based on the total weight of the solution.

[0044] Other materials may also be present in the process of preparingthe rubber modified monovinylidene aromatic polymer composition,including plasticizers, e.g. mineral oil; flow promoters, lubricants,antioxidants, catalysts, mold release agents, or polymerization aidssuch as chain transfer agents, including alkyl mercaptans, e.g.n-dodecyl mercaptan. If employed, a chain transfer agent can be presentin an amount of from about 0.001 to about 0.5 weight percent based onthe total weight of the polymerization mixture to which it is added.

[0045] The temperature at which the polymerization is conducted willvary according to the specific components, particularly initiator, butwill generally vary from about 60 to about 190° C.

[0046] Crosslinking of the rubber in the resulting product and removalof the unreacted monomers, as well as any solvent, if employed, andother volatile materials is advantageously conducted employingconventional techniques, such as introducing the polymerization mixtureinto a devolatilizer, flashing off the monomer and other volatiles atelevated temperature, e.g. from 200 to 300° C. under vacuum and removingthem from the devolatilizer.

[0047] Typically, a bimodal composition is produced by polymerizing afeed of the desired components and a grafting initiator in a series ofreactors, wherein the rubber particles are formed and stabilized withinthe first reactor, then fed to the top of a second reactor, wherein asecond feed is added. The second feed may already contain sized rubberparticles or may be another monomer/rubber raw material feed which willproduce large particles. Methods of preparing bimodal particle sizepolymers are disclosed in U.S. Pat. No. 5,240,993, which is incorporatedherein by reference, and in EP-0096447.

[0048] As used herein, the volume average particle size refers to thediameter of the rubber particles, including all occlusions of vinylaromatic polymer within the rubber particles. Volume average particlesizes and distributions may be measured using conventional techniquessuch as a Coulter Counter™, transmission electron microscopy.

[0049] The phosphorus-containing compound in the flame retardantcopolymer of the present invention is employed in amounts of at leastabout one(1)parts by weight, preferably at least about two(2)parts byweight, and more preferably at least about five(5) parts by weight basedon 100 parts by weight of the polymer composition of the presentinvention. In general, the phosphorus-containing compound in the flameretardant copolymer of the present invention is amounts less than orequal to about thirty (30) parts by weight, preferably less than orequal to about fifteen (15) parts by weight, more preferably less thanor equal to about 13 parts by weight, and most preferably less than orequal to about ten (10) parts by weight based on 100 parts by weight ofthe copolymer of the present invention.

[0050] In addition, the flame retardant polymer compositions may alsooptionally contain one or more additives that are commonly used inpolymers of this type. Preferred additives of this type include, but arenot limited to: antioxidants; impact modifiers; plasticizers, such asmineral oil; antistats; flow enhancers; mold releases; fillers, such ascalcium carbonate, talc, clay, mica, wollastonite, hollow glass beads,titanium oxide, silica, carbon black, glass fiber, potassium titanate,single layers of a cation exchanging layered silicate material ormixtures thereof, and perfluoroalkane oligomers and polymers (such aspolytetrafluoroethylene) for improved drip performance in UL 94.Further, compounds which stabilize flame retardant polymer compositionsagainst degradation caused by, but not limited to heat, light, andoxygen, or a mixture thereof may be used.

[0051] If used, the amount of such additives will vary and need to becontrolled depending upon the particular need of a given end-useapplication, which can easily and appropriately be exercised by thoseskilled in the art.

[0052] The flame retardant copolymers of this invention arethermoplastic. When softened or melted by the application of heat, theflame retardant polymer compositions of this invention can be formed ormolded using conventional techniques such as compression molding,injection molding, gas assisted injection molding, calendering, vacuumforming, thermoforming, extrusion and/or blow molding, alone or incombination. The flame retardant polymer compositions can also beformed, spun, or drawn into films, fibers, multi-layer laminates orextruded sheets, or can be compounded with one or more organic orinorganic substances, on any machine suitable for such purpose.

[0053] The copolymers of the present invention are useful to fabricatenumerous useful articles and parts. Some of the articles which areparticularly well suited include television cabinets, computer monitors,related printer housings which typically are required to have excellentflammability ratings.

[0054] The following examples are provided to further illustrate theinvention and should not be construed as limiting its scope.

EXAMPLES Example 1Bis(2-oxo-5,5-dimethyl-1,3,2-dioxaphosphorinanylmethyl) Fumarate (ODDPMFumarate)

[0055] ODDPM alcohol (36.03 g, 02.00 mole) was added to 100 mL of drychloroform in a 3-neck, 250 mL round bottom flask. The middle neck wasfitted with a reflux condenser which was fitted with a drying tubecontaining sodium sulfate. The outer necks were fitted with glassstoppers. The mixture was stirred with a magnetic stirbar, and when theODDPM alcohol had fully dissolved in the chloroform, fumaryl chloride(15.30 g, 0.100 mole) was added all at once to the solution. The mixturewas detected by sampling the atmosphere above the condenser withpHydrion paper (pH 0-13). The pH paper turned deep red which indicated apH of 0. Also, after five hours of reaction time, an increase insolution viscosity was observed relative to that of the initialsolution. The solution was then allowed to cool to room temperature, and75 mL of chloroform was added to the flask. The solution was transferredto a 250 mL separatory funnel and added dropwise to a large excess ofbenzene. A white translucent solid precipitated from the benzene whichwas collected by Büchner filtration, washed with benzene, and dried in avacuum oven overnight at 60° C. The yield of ODDPM methacrylate was 39.0g (89 percent). The ODDPM methacrylate (m.p. 149.5-150° C.) was purifiedby recrystallization from benzene/chloroform.

Example 2 Copolymerization of Styrene andBis(2-Oxo-5,5-dimethyl-1,3,2-dioxaphosphorinanylmethyl)Fumarate

[0056] ODDPM fumarate is not soluble in non-polar hydrocarbon solvents,but has sufficient solubility in halogenated solvents such aschloroform. The copolymerization solutions were prepared in round bottomflasks by first adding the appropriate amount of AIBN from an AIBNstandard solution made from 0.200 g AIBN and 29.8 g chloroform. Then,the monomers were added followed by dilution with chloroform (Table 1).For the copolymerizations with comonomer feed compositions of greaterthan 10 mole percent ODDPM fumarate homogeneous solution could only beachieved at elevated temperatures. The round bottom flasks were cappedwith rubber septa, which were fastened tightly to the flasks with copperwire. Prior to polymerization, each solution was sparged with N₂ for 10minutes while being chilled with ice water. The flasks were then placedin an oil bath at 60° C. (+/−0.5° C.) for the times given in Table 1.The copolymerization solutions were concentrated on a Rotovaporapparatus and added to a large excess of methanol to precipitate thecopolymers. The copolymers were collected by gravity filtration, washedwith methanol, and dried in a vacuum oven at approximately 80° C.overnight. The poly(styrene-co-ODDPM fumarate) samples were dissolved inchloroform and purified further by reprecipitation in diethyl ether.Finally, the copolymers were collected by gravity filtration, washedwith diethyl ether, and dried in a vacuum oven at approximately 80° C.overnight. The copolymers all had a powdery texture. TABLE 1Formulations for the Copolymerizations¹ of Styrene and ODDPM Fumarate at60° C. Mole % ODDPM ODDPM Fumarate in Fumarate CHCl₃ Reaction FeedStyrene (g)/(mol) (g)/(mold) (g) Time (hr.)  5 2.47/2.38 × 10⁻²0.55/1.25 × 10⁻³ 25.7 7.5 10 2.34/2.25 × 10⁻² 1.10/2.50 × 10⁻³ 25.3 9.015 2.21/2.13 × 10⁻² 1.65/3.75 × 10⁻³ 24.9 7.5 20 2.08/2.00 × 10⁻²2.20/5.00 × 10⁻³ 24.5 7.0 30 1.82/1.75 × 10⁻² 3.30/7.50 × 10⁻³ 23.6 6.5

What is claimed:
 1. A phosphorus-containing compound suitable for use asa comonomer, capable of being copolymerized with a monovinylidenearomatic compound to impart flame resistant properties to the resultantcopolymers thereof, comprising compounds of a generic formula:

wherein: R₁ is hydrogen or an alkyl; R₂ is carboalkoxy; X is oxygen,sulfur or alkylamine; Y is oxygen or sulfur; P is pentavalent phosphorus; and n is 2or3.
 2. A phosphorus-containing compound suitable for use asa comonomer, capable of being copolymerized with a monovinylidenearomatic compound to impart flame resistant properties to the resultantcopolymers thereof, comprising compounds of a generic formula:

wherein: R₁ is hydrogen or an alkyl; R₂ is carboalkoxy; X is oxygen,sulfur or alkylamine; P is trivalent phosphorus ; and n is 2 or
 3. 3. Aphosphorus containing compound of claim 1 wherein R₂ is a radical ofgeneric formula:

wherein: R₁ is hydrogen or an alkyl; X is oxygen, sulfur or alkylamine;Y is oxygen or sulfur; P is pentavalent phosphorus ; and n is 2 or
 3. 4.A phosphorus containing compound of claim 2 wherein R₂ is a radical ofgeneric formula:

Wherein: R₁ is hydrogen or an alkyl; X is oxygen, sulfur or alkylamine;P1 P is trivalent phosphorus ; and n is 2 or
 3. 5. A phosphoruscontaining compound of claim 1 which isbis(2-oxo-5,5-dimethyl-1,3,2-dioxaphosphorinanylmethyl) fumarate.